Reproductive behavior in Drosophila will be studied by genetic and molecular biological approaches. By analyzing (a) the effects of mutations causing anomalies in courtship and mating behavior, and (b) the action of the genes defined by such variants, it is hoped that insights about the "genetic programming" of the flies to perform species-specific fixed action patterns can be gained. "Courtship mutations" can be more than that: (a) they might cause other kinds of sharply defined defects (see below); (b) behavioral/neural mutants initially isolated on non- reproductive criteria often lead to particular abnormalities of male- female interactions. Thus, another angle from which to view the reproductive-genetic studies concerns pleiotropies, or "gene versatilities", and generalities that may emerge from these investigations -- keeping in mind that analogous stories are emerging from neurogenetic studies involving vertebrates (hence, a possible long- range "health relevance" of the experiments on Drosophila). The molecular sides of certain courtship-genetic projects has allowed speciation and evolutionary issues to be addressed by characterizing naturally occurring genetic variations and by bioassaying them in behavioral settings. The specific genes to be studied are: (a) no-on- transient-A/dissonance [its effects on courtship song and visual behavior: in-vitro mutagenesis of intragenic regions, including those that could have nucleic-acid binding activity -- augmented by immunohistochemical experiments; determination of effects of hypothetically null and conditional mutations; dissection of the "local relevance" of nonA expression with regard to the subsets of the phenotypic defects; isolation of interspecific nonA variants and putative intraspecific ones]; (b) cacophony [relationship of this song mutant, and a newly isolated cac singing-defective mutation -- via cloning and locus- identification -- to visual-defect and embryonic lethal mutants, which are connected to cac by complementation patterns; mosaic analysis of putative thoracid neural vs. muscular foci for the song defect]; (c) fruitless [locus-identification, aided by 3 transposon tagged partial-fru mutants; assessment of reporter-gene expression in 2 of these mutants, against a background of fru-associated pleiotropy (behavioral sterility, aberrant courtship song, anomalous inter-male courtships, defective male- specific muscle development); has a loss-of-function mutant been generated as a viable, behaviorally defective, fru-synthetic deletion, or do certain lethal variants at the locus represent the null phenotype?]; (d) a new autosomal male-near-sterile [analysis of behavioral defects, including possibly auditory or chemosensory ones; isolation of new alleles; initiation of locus isolation, given transposon-tagged nature of the original mutation]; (e) period [bioassays of D. melanogaster and D. simulans per clones, in courtship experiments related to "sender-receiver coupling" hypothesis; inferences on adaptive significance of intraspecific per variability, via assessment of a putative geographical cline.]